The following experimental approaches will be undertaken: 1) Further examination of nature of the increase in tyrosine hydroxylase activity. By an immunoprecipitation technique it will be established whether new synthesis of tyrosine hydroxylase molecules is elicited by hypoxia or hypercapnia. The involvement of second messengers in tyrosine hydroxylase induction which may be activating specific protein kinases will be investigated. 2) Studies on the role of type II cells in the regulation of chemoreceptors with the possible involvement of specific amino acids such as GABA, glycine and taurine will be done. 3) The responsiveness of chemoreceptors to hypoxia in carotid body of spontaneous hypertensive rats (SHR) will be studied.